They apply more to candidates whose main selling points are insane charisma and charm, rather than a solid record. Incumbents have the easiest time being believed, as long as what they say is a continuation of what they did in office. When Sarkozy promises to get tough on crime or to gut immigrants' rights, I can compare what he says to what he did during the riots. When Royal promises to keep the 35-hour week a few months after she promised to repeal it, I reserve the right to doubt her credibility.